Enhanced wireless communication for medical devices

ABSTRACT

Methods and apparatuses for wireless communication between medical devices are provided. In some embodiments, commodity low power, low bandwidth communication protocols may be utilized to simultaneously convey multiple signals with high fidelity and reliability. For example, cardiac sound data and ECG data may be compressed using a common ADPCM component and inserted into a common BLE packet structure. Command-control data may also be inserted. Where required command-control data reporting frequency is less than the packet frequency, header bits may be utilized to convey multiple types of command-control data in a given packet byte position. Rolling packet sequence values may be inserted into the common packet structure, for use by receiving devices to identify link integrity failures.

TECHNICAL FIELD

The present disclosure relates to medical devices utilizing wirelesselectronic communications. More specifically, this disclosure relates tomethods and apparatuses for enhancing wireless communications in medicaldevice applications, such as wireless cardiac sensors.

BACKGROUND

Use of wireless communications techniques for electronic devices isbecoming increasingly popular. Wireless devices provide convenience andease of use. Bluetooth has become particularly prevalent as a wirelesscommunications protocol. It provides versatile mechanisms fortransmitting digital signals over short distances with very low powerconsumption. Bluetooth has become a ubiquitous standard amongst mobilephones, tablet computers, personal computers, wireless headphones,automobiles, and a wide variety of other device types. As a result,Bluetooth devices are readily interoperable with other electronicdevices. Meanwhile, high production volumes result in ready availabilityand relatively low cost for transceiver chipsets and circuit boards,further reinforcing the widespread adoption of the standard.

Bluetooth Low Energy (“BLE”) is a subprotocol defined within theBluetooth 4.0 protocol, that enables highly energy-efficient transfer ofdata between a client device (e.g. a sensor) and a server device (e.g. amobile phone or personal computer). BLE can be particularly valuable forbattery-operated devices, for which minimizing power consumption may becritical.

While the prevalence of Bluetooth and power-efficiency of BLE providemany advantages, some device types, particularly in the context ofmedical instrumentation, give rise to communication requirements thatmay not be well-satisfied by standard Bluetooth implementations. Forexample, many types of instrumentation may require transmission ofmultiple signal types, which would traditionally be conveyed by multiplewires or multiple wireless radios. However, consumer electronic devicesmay be limited in the number of radios provided, while sensors withmultiple radios may require greater power consumption, resulting inlarger batteries and/or worse battery life. Meanwhile, BLE bandwidthlimitations may impact sensor performance. For example, while humans cantypically perceive sounds ranging from about 20 Hz to about 20 kHz, BLEas a protocol does not have enough bandwidth to transmit the entirety ofthe human audio spectrum, due to small packet size and slow packetspeed. Traditional Bluetooth and BLE implementations may be particularlydisadvantageous or limiting for medical devices such as wireless cardiacdevices.

SUMMARY

Improved implementations of BLE-based wireless communication protocolscan provide high levels of performance in wireless medical deviceapplications, while still enabling use of commodity Bluetoothtransceiver hardware and commodity host electronic devices.

In some embodiments, a method is provided for transmitting cardiac datafrom a wireless sensor to a host device. Cardiac sound data and ECG dataare received at a wireless sensor, such as via onboard transducersdigitizing audio and electrical signals sensed on a patient. The cardiacsound and ECG data can be filtered, such as via application of a digitallowpass filter to cardiac sound data to attenuate frequency componentsabove approximately 2 kHz. The cardiac sound data and ECG data arecompressed, such as through application of the data to an adaptivedifferential compression component. In some embodiments, a commonadaptive differential compression component can be applied to both thecardiac sound data and the ECG data. The compressed cardiac sound dataand compressed ECG data can be combined into a common packet structure,and transmitted from the wireless sensor to the host device.

The common packet structure may also include command-control data. Inembodiments where the packet frequency is greater than the requiredfrequency of command-control data reporting, command-control data mayinclude a header bit indicating one of multiple command-control datacontent types with which an associated command-control value isassociated—thereby reducing the number of bits that must be allocated tocommand-control data within the packet structure.

The common packet structure may also include mechanisms to identifywireless communication link integrity problems. A packet sequence value,such as a rolling four-bit value, can be inserted into each packet bythe transmitting device, such as a cardiac sensor. The receiving device,e.g. the host device, can decode the packet sequence value towardsensuring that sequentially-received packets have sequential packetsequence values. In the event that the receiving device identifies a gapin rolling packet sequence values, the receiving device may determinethe existence of a failure of the wireless communication link integrity.Such a failure may then be conveyed to a user via, e.g., displaying awarning indicia on a host device user interface.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic block diagram of a medical instrumentationenvironment including a wireless cardiac sensor and host device.

FIG. 2 is a schematic block diagram of a wireless packet structure.

FIG. 3 is a schematic block diagram of a cardiac signal processingchain.

DETAILED DESCRIPTION OF THE DRAWINGS

While this invention is susceptible to embodiment in many differentforms, there are shown in the drawings and will be described in detailherein several specific embodiments, with the understanding that thepresent disclosure is to be considered as an exemplification of theprinciples of the invention to enable any person skilled in the art tomake and use the invention, and is not intended to limit the inventionto the embodiments illustrated.

Techniques are described that can be used to effectively transmitmedical device data, particularly heart diagnostic data, via alow-power, low-bandwidth wireless communications protocol such asBluetooth Low Energy. Several techniques described hereinbelow can beapplied individually or in combination.

FIG. 1 illustrates a typical operating environment in which embodimentscan be employed. Cardiac sensor 100 is a wireless heart monitor capableof detecting multiple types of diagnostic data, including heart soundsand ECG electrical recordings. Sensor 100 includes microprocessor 102for processing and storing data from transducers 103 into memory 104.Sensor transducers 103 can include audio transducer 103A, forauscultation such as recording of heart sounds, and ECG transducer 103B,for monitoring of cardiac electrical activity. Bluetooth transceiver 105is in operable communication with processor 102 in order to convey datato and from remote electronic devices, such as host device 120. Battery106 is a rechargeable battery supplying power to sensor 100. In order tomaximize the duration between required charges, and minimize the size,weight and expense of sensor 100, sensor 100 is designed for low powerconsumption during operation.

Sensor 100 communicates via wireless data connection 110 with hostdevice 120. Host device 120 may preferably be a standard, commoditymobile wireless computing device, such as a smartphone (e.g. AppleiPhone™), tablet computer (e.g. Apple iPad™), or laptop computer. Hostdevice 120 includes microprocessor 122 for processing and storing data.Bluetooth transceiver 123 enables wireless communication betweenprocessor 122 and external devices, such as sensor 100. Host device 120further includes user interface components 124 (such as a touchscreen),memory 125 for data storage, and battery 126. While illustrated as amobile device in the embodiment of FIG. 1, in other embodiments, hostdevice 120 could alternatively be selected from amongst other types ofcomputing devices having a Bluetooth transceiver, such as a personalcomputer or a central sensor monitoring station.

The BLE protocol may be desirable for implementation of wirelesscommunications link 110, in order to minimize energy consumption duringoperation and therefore extend the battery life of sensor 100 and hostdevice 120. However, BLE, as commonly implemented, presents significantlimitations in a wireless cardiac sensor environment. One suchlimitation is bandwidth. Common mobile devices 120 have limitations inpacket rate utilizing the BLE protocol for communications link 110. Forexample, some mobile phones may have a theoretical minimum packetinterval at which one BLE packet can be accepted every 5 milliseconds.Exacerbating this limitation is a need in medical applications for highdata integrity and reliability. In such embodiments, it may not bedesirable to potentially sacrifice data integrity and link reliabilityby requiring data transmission at or near theoretical maximum packetrates. While decreasing packet rate may provide better packet intervaloperating margin, bandwidth constraints are even more limiting. Withsome common consumer mobile devices, it has been found that reliable BLEcommunications can be maintained sending packets at 8 ms intervals.

BLE also imposes packet size constraints. Moreover, regardless ofprotocol constraints on packet size, it may be further desirable toreduce packet size in order to reduce power consumption. Meanwhile, inorder to implement an effective wireless cardiac sensor providing bothauscultation and ECG data, packets will preferably accommodate multipledata streams, such as heart sound audio data from audio transducer 103A,ECG data from transducer 103B, and command-and-control data associatedwith the operation of cardiac sensor 100 and its interaction with hostdevice 120. Packet efficiency may be critical to use of BLE in suchenvironments.

FIG. 2 illustrates an optimized BLE packet structure that may beutilized in communications from cardiac sensor 100 to host device 120.The packet structure of FIG. 2 is optimized to convey multiple types ofmedical instrument and control data via a relatively low-bandwidth andlow-power BLE communication link that can be reliably received bystandard smartphones, tablets or other consumer electronic devices.Specifically, the packet structure of FIG. 2 conveys heart sounds, ECGdata and command/control data simultaneously, with clinical fidelity,within a single BLE packet, using one standard BLE radio set.

Each packet 200 in FIG. 2 is preferably formed having a byte lengthprovided for by BLE standards, and packet intervals preferablycompatible with commodity BLE chipsets and computing devices. Such adata structure may provide an effective bitrate of approximately 20kbps.

Packet 200 includes header bytes 210, command and control bytes 220, andcardiac data 230. In the illustrated embodiment, cardiac data 230includes audio payload 232 and ECG payload 234. Audio payload 232 isutilized for transmitting heart sound data recorded by audio transducer103A. FIG. 3 illustrates a schematic representation of cardiac signalprocessing components within cardiac sensor 100, which operate togenerate data conveyed in the BLE packet structure of FIG. 2. Audiosensor 300 converts an audio signal, such as cardiac auscultation, intoan analog electronic signal. Analog-to-digital converter (ADC) 310samples the output of sensor 300 and generates a digital data stream311. ADC 310 initially samples acoustic heart sound signals at anapproximately 4 kHz sample rate, with 16-bit samples, yielding a 64 kbpsaudio stream. Audio compression is applied by adaptive differentialpulse-code modulation (ADPCM) encoder 330 to yield a 4-bit audio stream332 at a 4 kHz rate (i.e. one 4-bit sample each 0.25 ms). Therefore,with an 8 ms packet interval, each packet 200 includes audio payload 232having 32 4-bit audio samples.

Digital filters 320 can be applied to the output 311 of ADC 310 prior toADPCM encoder 330 in order to reduce artifacts and distortion during theADPCM compression process. In particularly, filters 320 will includestrong low-pass filters to eliminate or drastically attenuate highfrequency components above the 2 kHZ range. It has been determined thatfrequency range limitations imposed by aggressive pre-filtering ofcardiac auscultation sounds before ADPCM compression is preferable forpurposes of human medical diagnostics, as compared to less aggressivefiltering accompanied by potential introduction of compression noise andartifacts by ADPCM encoder 330.

Another advantage of the packet structure of FIG. 2, particularly givenlimitations on packet interval in common smartphones and other mobiledevices that may be utilized as host device 120, is that it combinesheart sound and ECG data within a single BLE packet. FIG. 3 furtherillustrates a schematic representation of an ECG data pipeline that maybe implemented on cardiac sensor 100. In use, ECG sensors 340 areconnected to a patient, and output electrical signals 341 indicative ofa patient's cardiac electrical activity.

Cardiac electrical signals 341 are sampled by analog-to-digitalconverter 350. In an exemplary embodiment, ADC 350 may generate 16-bitsamples at a 500 Hz sampling rate. This yields a digital ECG data stream351 having a data rate of 8 kbps, to which filter 360 may be applied.Utilizing an 8 ms BLE packet interval, ECG data stream 351 wouldtherefore require 8 bytes within each BLE packet. However, given theamount of packet 200 allocated to cardiac audio data, as describedabove, it may be desirable to compress the ECG data stream, provided thecompression can be achieved without material negative impact on the ECGdata fidelity.

It has been determined that the same ADPCM encoder 330 used to encodecardiac audio data, can also be effectively utilized to reduce ECG databandwidth without significant negative impact on the ECG signal fidelityvia strategic specification of sample rate. By selecting a 500 Hz samplerate, measurement differentials between adjacent samples in a typicaldigitized ECG signal are such that the ECG data stream may beeffectively encoded by ADPCM encoder 330 to yield an encoded ECG datastream 334 that reduces the size of ECG payload 234.

In some embodiments, audio sensor 300 and ADC 310 can be implementedwithin audio transducer 103A, ECG sensors 340 and ADC 350 can beimplemented within ECG transducer 103B, with filter 320, filter 360 andencoder 330 being implemented by processor 102. In other embodiments,the elements of FIG. 3 can be distributed differently amongst componentssuch as audio transducer 103A, ECG transducer 103B, processor 102,custom ASICs, GPUs, or other components.

Bandwidth-efficient conveyance of command and/or control data (sometimesreferred to as command-control data) may also be important in wirelesscardiac sensor and other medical device applications. Forcommand-control data of a nature that the acceptable reporting frequencyis less than the packet frequency, it may be desirable for sequentialpackets to transmit different command-control data content types withinthe same packet bit positions. A header bit or bits may be utilized toindicate which of multiple types of command-control data is conveyedwithin associated packet bit positions.

For example, in the context of a wireless cardiac sensor transmitting atan 8 ms packet interval, it may not be necessary to transmit certaincommand-control data, such as volume level or battery level, at 8 msintervals. Longer intervals may be sufficient, while still ensuringusers perceive a high level of responsiveness. Thus, in the packetstructure of FIG. 2, bits within header 210 can be utilized to conveyone of multiple content types of command-control data. For example, aheader bit may be utilized to indicate whether the data within commandand control data 220 reflects a volume level or battery level. Dependingon the number of bits required for sufficient command-control data valuegranularity, and the desired frequency of command-control dataconveyance, in other embodiments, multiple header bits can be utilizedto enable greater numbers of command-control data content types to beconveyed within a given packet byte position. For example, in anotherembodiment, two bits may be used to specify one of four differentcommand-control data content types, with associated bit positionsconveying an associated value. In some embodiments, header bits may beconveyed in different byte positions from associated command and controlvalues within packet 200; in other embodiments, header bits andassociated command and control values may be conveyed within the samebyte position of packet 200, thereby intermixing header data 210 andcommand and control data 220.

Another important aspect of wireless communications in some medicalapplications is verifying link integrity. For high risk data such asheart sound and ECG data, it may be desirable for devices to rapidly andreliably alert the user when a data transmission quality problem arises.By effectively identifying data transmission issues, a user can promptlyremedy equipment problems and ensure that anomalous results areattributed to instrumentation error rather than the patient beingmonitored. However, traditional BLE protocols do not provide mechanismsto determine when packets are dropped.

Therefore, the packet of FIG. 2 preferably includes a link integrityverification mechanism integrated within the packet structure.Predetermined bits within header 210 can be allocated to a rollingpacket sequence indicator. When transmitted by cardiac sensor 100,processor 102 constructs consecutive packets to increment through arolling multi-bit packet sequence value. The receiving device 120 canthen decode the packet sequence value to verify that consecutive packetsare received with sequentially incrementing packet sequence values. Inthe event that packet sequence values are not sequential in adjacentpackets, receiving device 120 can determine that the integrity of link110 has been compromised, and alert a user to the issue by, e.g.,displaying an appropriate warning indicia on user interface 124. Theembodiment of FIG. 2 utilizes a rolling packet sequence value that isfour bits in length, which in some embodiments may be an optimaltradeoff between minimizing failures to identify link integrity problems(for which longer sequence values are better), and minimizing powerconsumption and bandwidth attributed to the link integrity verificationfunction (for which shorter sequence values are better).

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the inventiondisclosed herein. Various modifications to these embodiments will bereadily apparent to those skilled in the art, and the generic principlesdefined herein may be applied to other embodiments without departingfrom the spirit or scope of the disclosure. Thus, the present disclosureis not intended to be limited to the embodiments shown herein but is tobe accorded the widest scope consistent with the principles and novelfeatures disclosed herein. All references cited herein are expresslyincorporated by reference.

1. A method for collecting diagnostic data from a heart of a subject,comprising: (a) using a monitoring device comprising an ECG sensor andan audio sensor to measure ECG data and audio data from said heart ofsaid subject; (b) transmitting said ECG data and audio data wirelesslyto a computing device separate from said monitoring device; and (c)using said computing device to process said ECG data and audio data toprovide an output indicative of said state or condition of said heart ofsaid subject.
 2. The method of claim 1, further comprising, prior to(b), compressing said ECG data and said audio data.
 3. The method ofclaim 1, further comprising, prior to (b), filtering said ECG data andsaid audio data.
 4. The method of claim 3, wherein said filteringcomprises attenuating frequency components above 2 kHz.
 5. The method ofclaim 1, further comprising (i) determining that a wirelesscommunication link between said computing device and said monitoringdevice has been compromised, and (ii) displaying a warning on a userinterface of said computing device, which warning is indicative of acompromise in said wireless communication link.
 6. The method of claim1, further comprising, prior to (b), using said ECG data and said audiodata to generate a common packet structure.
 7. The method of claim 6,further comprising inserting a rolling packet sequence into said commonpacket structure.
 8. The method of claim 7, further comprising (i)receiving at said computing device a sequential data packet having anon-sequential rolling packet sequence, and (ii) displaying a warning ona user interface of said computing device, which warning is indicativeof a compromise in a wireless communication link between said monitoringdevice and said computing device.
 9. The method of claim 6, wherein saidcommon packet structure comprises command-control data.
 10. The methodof claim 9, wherein said command-control data is present at a reportingfrequency that is lower than a data packet frequency corresponding tosaid ECG data and/or said audio data.
 11. The method of claim 9, whereinsaid command-control data comprises a header value indicative of acontent type of said command-control data.
 12. The method of claim 1,wherein said ECG data and said audio data are transmitted from saidmonitoring device to said computing device via radio frequencycommunication.
 13. The method of claim 1, wherein said ECG data and saidaudio data are transmitted from said monitoring device to said computingdevice via a Bluetooth Low Energy communications link.
 14. The method ofclaim 1, further comprising storing said ECG data and said audio data onsaid monitoring device.
 15. The method of claim 1, further comprisingidentifying a data transmission issue with transmitting said ECG dataand said audio data to said computing device.
 16. The method of claim 1,wherein said computing device is a mobile computing device.